1. Field of the Invention
The present invention relates to a three-dimensional shape measuring apparatus for measuring a three-dimensional shape of an object to be measured (hereinafter, called as “measurement object”) in a non-contact state.
2. Description of the Related Art
A method for measuring a three-dimensional shape of a measurement object with use of a non-contact three-dimensional shape measuring apparatus is utilized in various industrial fields e.g. computer graphics, designing, or automobile manufacturing. Examples of the measurement principle to be used in the three-dimensional measurement include a light cutting method using laser slit light or the like, a pattern projecting method using pattern light, a stereoscopic method based on images obtained by imaging a measurement object with a camera in different viewpoints, and a moire method using a moire technique. Three-dimensional data such as polygon data is derived based on the measurement data obtained by the aforementioned methods.
Measurement data concerning the shape of the measurement data, which is obtainable by a one-time measurement, is limited in any of the aforementioned methods. In view of this, in case of measuring the shape of a measurement object having large dimensions, a lens element having a large field of view (FOV) is used, or a distance from the measuring apparatus to the measurement object is increased, or a like approach is adopted to increase the measurement dimensions to be used in measuring the shape of the measurement object by a one-time measurement. However, since measurement dimensions and measurement precision have a relation of trade off, it is not desirable to increase the field of view, or the distance from the measuring apparatus to the measurement object, without considering the relation.
In view of the above, there is proposed an approach of measuring the shape of a measurement object multiple times while shifting the measurement dimensions in such a manner that at least portions of consecutive measurement dimensions by the shifting are lapped one over the other to measure the shape of the single measurement object. With use of this approach, most proximate points in the overlap portions are searched based on the acquired information by a software; position adjustment i.e. data registration is performed in such a manner as to minimize the sum of the measurement data errors; and the multiple measurement data are synthesized i.e. merged into single data.
Examples of the well-known data integration methods are e.g. as follows:
(i) a method for designating corresponding points among multiple measurement data to be integrated by a user's manual operation;
(ii) a method for setting reference information with respect to a measurement object or its vicinity (in Japanese Unexamined Patent Publication No. Hei 7-260452, plural spherical members are disposed in an overlap area where a measurement object is imaged in an overlap manner, and information relating to the center positions of the spherical members is used as reference information);
(iii) photogrammetry, in which markers are attached to a measurement object, information relating to the positions of the markers is obtained in advance by photogrammetry or a like technique, and the obtained information is used as reference information (in Japanese Unexamined Patent Publication No. 2004-220510, target markers having different color scheme patterns are used); and
(iv) a method for estimating the position and posture of the measuring apparatus, and using the estimative information as reference information.
In any of the integration methods, the multiple measurement data concerning the overlap portions are handled equally. Accordingly, if degraded data e.g. data with much noise or a large measurement error is included in at least one of the measurement data, accurate data registration may be impossible. In order to avoid such a drawback, the user may manually select and erase the degraded data prior to data integration, which involves a cumbersome operation. Further, this operation requires a user's skill of judging the quality of the acquired data.